—We study the multicast provisioning problem in transparent optical networks with Mixed Line Rates. For each multicast session, light-trees with different line rates are used to route the traffic demands. We aim at minimizing the joint cost of transponders and wavelength channels in the light-trees for routing multicast sessions. However, different line rates are subject to different maximum transmission reaches. Besides, the line rate selection, routing and wavelength assignment problems should be solved simultaneously, what makes light-tree optimization complicate. In light of this, we formulate the multicast provisioning problem as a Mixed Integer Linear Programming (MILP). Simulation results validate our model and show that both the transponder cost and the wavelength channel cost can be saved by flexibly using mixed line rates for provisioning multicast communications. Index Terms—Optical Networks, Mixed Line Rate (MLR), Multicast Routing and Wavelength Assignment (MRWA), Light-tree, Integer Linear Programming (ILP)